///Convert the \c Value of a maps to another type.

   ///This \ref concept::ReadMap "read only map"

   ///converts the \c Value of a maps to type \c T.

   ///Its \c Value is inherited from \c M.

   ///

   ///Actually,

   ///\code

   ///  ConvertMap<X> sh(x,v);

   ///\endcode

   ///it is equivalent with

   ///\code

   ///  ConstMap<X::Key, X::Value> c_tmp(v);

   ///  AddMap<X, ConstMap<X::Key, X::Value> > sh(x,v);

   ///\endcode

   ///\bug wrong documentation

   template<class M, class T> 

   class ConvertMap

   {

     const M &m;

   public:

     typedef typename M::Key Key;

     typedef T Value;

     ///Constructor

     ///Constructor

     ///\param _m is the undelying map

     ///\param _v is the convert value

     ConvertMap(const M &_m) : m(_m) {};

     Value operator[](Key k) const {return m[k];}

   };

   ///Returns an \ref ConvertMap class

   ///This function just returns an \ref ConvertMap class.

   ///\relates ConvertMap

   ///\todo The order of the template parameters are changed.

   template<class T, class M>

   inline ConvertMap<M,T> convertMap(const M &m) 

   {

     return ConvertMap<M,T>(m);

   }